Global warming which is driven by human behavouir is causing temperatures to rise in oceans resulting in coral bleaching as coral only survive in certain temperatures. Coral bleaching disrupts food webs and then leads to extinction of species. Global warming can also cause ice to melt making sea levels to rise and therefore coral wont survive as they live in shallow waters. Global warming leads to ocean acidification which is when the water absorbs too much carbon dioxide. The ph change in the water affects the coral and can lead to bleaching.
As the demand for fish is increasing as more people want it in their diet. This demand for fish means more fishing which leads to overfishing, this means too many fish are being fished including juvenlilles; meaning they arent having time to reproduce. Leading to extinction of the fish. Some methods of fishing can be harmful to coral and cause coral bleaching.
Tourism is important for developing countries to earn money. However recreational activities like diving, surfing and water skiing are causing harm to coral. Which leads to coral bleaching and therefore food webs are disrupted. Coral reefs are also harmed by the pollutants and sewage put into the water from local hotel resorts. Tourists also take away parts of the coral to keep as ornaments which again causes coral bleaching. On yacht trips anchors are often dropped on coral reefs which is also destructive.
Sedimentation is caused by erosion from construction/mining/farming/logging. The increase in sediment can smother coral and block their sunlight which prevents them from photosynthesis. The coral can also mistake sediment for food which they eat and then die.